A fluorescent lamp (also called a fluorescent tube) uses electrical current to excite a vapor within a glass tube resulting in the discharge of electrons. Visible light is produced when the electrons cause a material coating the inner wall of the glass tube to fluoresce. Linear fluorescent lamps are routinely used in commercial or institutional buildings, and are commonly installed in troffer light fixtures (recessed troughs installed in a ceiling) and pendant light fixtures (housings suspended from a ceiling by a chain or pipe).
Fluorescent lamps have been steadily replacing incandescent lamps in many lighting applications. Compared to an incandescent lamp, a fluorescent lamp converts electrical power into useful light more efficiently, delivers a significantly longer useful life, and presents a more diffuse and physically larger light source. However, fluorescent lamp technology has disadvantages. A fluorescent lamp is typically more expensive to install and operate than an incandescent lamp because the fluorescent lamp requires a ballast to regulate the electrical current. Fluorescent light fixtures cannot be connected directly to dimmer switches intended for incandescent lamps, but instead require a compatible dimming ballast. The performance of fluorescent lamps may be negatively impacted by environmental conditions such as frequent switching and operating temperatures. Many fluorescent lamps have poor color temperature, resulting in a less aesthetically pleasing light. Some fluorescent lamps are characterized by prolonged warm-up times, requiring up to three minutes before maximum light output is achieved. Also, if a fluorescent lamp that uses mercury vapor is broken, a small amount of mercury (classified as hazardous waste) can contaminate the surrounding environment.
Digital lighting technologies such as light-emitting diodes (LEDs) offer significant advantages over traditional linear fluorescent lamps. These include, but are not limited to, better lighting quality, longer operating life, and lower energy consumption. Increasingly, LEDs are being designed to have desirable color temperatures. Moreover, LEDs do not contain mercury. Consequently, a market exists for LED-based retrofit alternatives to legacy lighting fixtures that use fluorescent lamps. However, a number of installation challenges and costs are associated with replacing linear fluorescent lamps with LED illumination devices. The challenges, which are understood by those skilled in the art, include light production, thermal management, and installation ease. The costs, which are similarly understood by those skilled in the art, typically stem from a need to replace or reconfigure a troffer or pendant fixture that is configured to support fluorescent lamps to instead support LEDs.
By the very nature of their design and operation, LEDs have a directional light output. Consequently, employing LEDs to produce light distribution properties approximating or equaling the light dispersion properties of traditional lamps may require the costly and labor-intensive replacement or reconfiguration of the host light fixture, and/or the expensive and complexity-introducing design of LED-based solutions that minimize the installation impact to the host light fixture. Often material and manufacturing costs are lost in this trade off.
Another challenge inherent to operating LEDs is heat. Thermal management describes a system's ability to draw heat away from the LED, either passively or actively. LEDs suffer damage and decreased performance when operating in high-heat environments. Moreover, when operating in a confined environment, the heat generated by an LED and its attending circuitry itself can cause damage to the LED. Heat sinks are well known in the art and have been effectively used to provide cooling capacity, thus maintaining an LED-based light bulb within a desirable operating temperature. However, heat sinks can sometimes negatively impact the light distribution properties of the light fixture, resulting in non-uniform distribution of light about the fixture. Heat sink designs also may add to the weight and/or profile of an illumination device, thereby complicating installation, and also may limit available space for other components needed for delivering light.
Replacement of legacy lighting solutions may be complicated by the need to adapt LED-based devices to meet legacy form standards. For example, in a commercial lighting system retrofit, disposal of a replaced fluorescent lamp's fixture housing often is impractical. Consequently, retrofit lamps often are designed to adapt to a legacy fluorescent fixture, both functionally and aesthetically. Also, power supply requirements of LED-based lighting systems can complicate installation of LEDs as a retrofit to existing light fixtures. LEDs are low-voltage light sources that require constant DC voltage or current to operate optimally, and therefore must be carefully regulated. Too little current and voltage may result in little or no light. Too much current and voltage can damage the light-emitting junction of the LED. LEDs are commonly supplemented with individual power adapters to convert AC power to the proper DC voltage, and to regulate the current flowing through during operation to protect the LEDs from line-voltage fluctuations. The lighting industry is experiencing advancements in LED applications, some of which may be pertinent to certain aspects of replacing linear fluorescent lamps.
U.S. Pat. No. 6,739,734 to Hulgan discloses a method of retrofitting a fluorescent light fixture (e.g., four foot T12 or T8 lamps) with LED-based luminaires without requiring removal of the fixture housing. However, rather than maintain existing circuitry, the fixture is stripped not only of its fluorescent lamps but also of its wireway cover and ballast(s). U.S. Published Patent Application No. 2010/0033095 by Sadwick discloses an apparatus for replacing a fluorescent lamp that includes an electrical connector adapted to maintain the existing circuitry of the fixture, including the fluorescent ballast. A voltage converter, direct current (DC) rectifier, and LED light source included in the apparatus simulate the behavior of a fluorescent lamp in response to signals from the fixture's existing circuitry. However, the reference defines a lamp housing physically configured as a prosthetic replacement for a fluorescent lamp in the fixture, rather than as a less expensive non-tubular light-directing structure.
U.S. Pat. No. 6,936,968 to Cross et al., U.S. Pat. No. 6,997,576 to Lodhie, and U.S. Published Patent Application No. 2012/0147597 by Farmer and all disclose versions of an LED light tube adapted for use in troffer light fixtures. The Cross reference defines a cylindrical elongated transparent envelope holding at least one serial string of LEDs along its length. Similarly, the Lodhie reference discloses a substantially transparent hollow cylinder containing multiple LEDs arranged to form two LED arrays, and mounted along opposite sides of a substantially planar printed circuit board (PCB). The Farmer reference also defines a tubular structure, but employs one or more side light LEDs combined with gradient optics to achieve a selected emitted light intensity variation across the surface of the tube. Once again, all three references define a lamp housing physically configured as a prosthetic replacement for a fluorescent lamp in the fixture, rather than as a less expensive non-tubular light-directing structure.
Accordingly, and with the above in mind, a need exists for an effective and inexpensive fluorescent lamp replacement. More specifically, a need exists for a fluorescent lamp replacement that may be employed with minimal reconfiguration of the existing troffer or pendant light fixture that supported the replaced lamp. A fluorescent lamp replacement is needed that may be manufactured at less cost than conventional retrofit lamps. Furthermore, a need exists for a fluorescent lamp that meets or exceeds the performance characteristics of fluorescent lamps, but also delivers the advantages of digital lighting technology (e.g., energy efficiency, tailorable color temperatures).
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.